1. Historical versus Current Distribution. Northern two-lined salamanders
(Euryceabislineata) are the well-known “yellow
salamanders” of the northeastern United States and eastern Canada. This
species was one of the first North American salamanders formally given a Linnaean name
(Green, 1818), and the numerous nineteenth century synonyms (see Harlan, 1826a; Holbrook,
1840; Dumeril et al., 1854; Cope, 1889) indicate that the species was widespread and well
known to naturalists of that era. No subspecies are currently recognized.
However, until Jacobs (1987) raised southern two-lined salamanders (E.
cirrigera) and Blue Ridge two-lined salamanders (E. wilderae)
to full specific status, these forms were considered subspecies of northern two-lined
salamanders, so the historical distribution included the range of those species as
well. Some workers, such as Petranka (1998), still recognize southern two-lined
salamanders and Blue Ridge two-lined salamanders as subspecies of northern two-lined
salamanders. I support the elevation of southern two-lined salamanders and Blue
Ridge two-lined salamanders and, indeed, I believe both of those forms are polytypic
(Sever, 1999b,c). In this report, E. bislineata is considered to
include group C of Jacobs (1987), all Canadian populations (none were analyzed by
Jacobs), and additional populations assigned to the species by morphological or genetic
analysis in Ohio, West Virginia, and Virginia (Sever, 1989, 1999a, Mitchell and Reay,
1999). The distribution of northern two-lined salamanders, therefore, is from
Labrador and northern Québec and eastern Ontario, through New Brunswick and New
England to northern Virginia, west through eastern Ohio and the Kanawha River valley of
West Virginia (Sever, 1999a). In Canada, northern two-lined salamanders still have
not been recorded from Nova Scotia or Prince Edward Island. Sever (1999a) stated
that the distributional limits of the species in Canada are unclear, and that the range
of the species may actually be expanding. The boundaries between northern
two-lined salamanders and southern two-lined salamanders in Ohio (Guttman and Karlin,
1986) and Virginia (Mitchell and Reay, 1999) have been established by allozyme analysis,
and some geographic overlap occurs in both states. The specific identity of
Maryland populations has not been determined, but allozyme analysis indicates that two
genetically distinct, geographically overlapping forms occur (Miller and Hallerman,
1994). The contact zone in West Virginia has not yet been investigated by genetic
analysis, but overlap occurs in the Kanawha River Valley (Sever, 1999a,b).
Ecological studies are necessary in areas of sympatry between northern two-lined
salamanders and southern two-lined salamanders to determine how reproductive isolation is
maintained. Southern two-lined salamanders replace northern two-lined salamanders
in the southern Blue Ridge Mountains in southwestern Virginia (Dunn, 1926; Jacobs, 1987),
and no areas of sympatry are known (Sever, 1999a,c). Some studies on two-lined
salamanders published prior to Jacobs (1987) do not specify localities from which
specimens were examined; thus, the specific identity of animals used cannot be
determined. In the present account, an effort was made to restrict comments to
studies on populations within the range of northern two-lined salamanders as defined
above.

2. Historical versus Current Abundance. Green (1818), in the original
description of the species, simply reported: “Inhabits shallow waters; is found in
numbers early in the spring, and is very active.” DeKay (1842), however,
stated: "Although this species is said to be very common, both by Green and Harlan,
I have never had the good fortune to meet with it." In many late nineteenth
century and early twentieth-century reports, northern two-lined salamanders were
considered common to very common (e.g., Allen, 1868; Morse, 1904; Reed and Wright,
1909). Cope (1889) stated that the species was “very abundant in
Pennsylvania, and extends its range, with decreasing numbers, to Maine.” I
collected my first specimen in 1961; the animal was lying upside down under a log, along
a rivulet at the edge of a dirt road that was bordered by a fence-row of Osage
orange. In 40 yr of experience with the species, I find that northern two-lined
salamanders remain common to seasonally abundant in appropriate habitats.
Obviously, habitat destruction (deforestation, pollution, and siltation of streams) has
eliminated many populations, but northern two-lined salamanders ikely are lpresent in
most clean-water, small, rocky, woodland streams within its range. Weller and Green
(1997) report no indication of decline in Canada where for most of their range, northern
two-lined salamanders are the only stream-side salamanders. The post-glacial
dispersal of the species into Labrador and nearly to Hudson Bay in Québec and
Ontario indicates tremendous dispersal ability in such a small amphibian.

3. Life History Features. Much literature occurs on these topics, from the
first description of nesting in shallow streams (the usual situation) by H.H. Wilder
(1899) to the most recent report involving nests at depths of 9–13.5 m in a
mountain lake (Lake Minnewaska, Shawangunk Mountains, New York) by Bahret (1996).
However, Bishop's (1941b) account on the natural history of northern two-lined
salamanders in New York is still the most comprehensive available for the species.

A. Breeding.
Reproduction is aquatic.

i. Breeding migrations. As noted by Bishop (1941b), no marked seasonal movements,
such as those associated with mole salamanders (Ambystoma sp.), occur. In
summer, especially during wet periods and at higher altitudes, adults may wander far from
breeding areas in springs, seeps, and streams. Dry conditions, however, will cause
these animals to return to aquatic habitats, independently of any mating or breeding
behavior (see MacCulloch and Bider [1995] for an extensive study of summer movements of
northern two-lined salamanders in Québec). In the population that Bahret
(1996) discovered nesting at considerable depths in a lake, the adults stayed in the lake
the entire year. In any event, because the eggs are laid in water and the larvae
are aquatic, females will congregate at appropriate nesting sites. Oviposition
follows within 1 mo or so of mating, so males congregate at such sites as well. In
Ohio, congregations of males and females in appropriate mating/nesting areas sometimes
commence in fall prior to hibernation. The mating period is at its peak in March and
April after hibernation. Northern two-lined salamanders are relatively easy to
find in these generally wet, cool periods, and adults seem abundant at locales where they
are hard to find in mid summer. Mating occurs on land (Noble, 1929a), but it is not
unusual to find pairs under rocks in the middle of streams during daylight hours.
All adult females at mating/nesting sites are gravid with large, vitellogenic eggs; this
does not necessarily mean an annual breeding cycle. Non-breeding females have no
compelling reasons to reside at mating/nesting sites and compete with sexually active
individuals for food and shelter. The classic description of courtship and mating
in northern two-lined salamanders is by Noble (1929a), which includes the first
observations on any plethodontid of the tail straddle walk and use of courtship
glands.

ii. Breeding habitat. Although small, swift-flowing, rocky, woodland streams are
the most frequent nesting areas, nests can be found in a wide variety of aquatic
habitats. The occurrence of nests in deep lakes already has been noted (Bahret,
1996), and I have found nests in gravelly spring-heads, wells, and boggy areas.

B. Eggs.

i. Egg deposition sites. In eastern Ohio, I commonly find the first nests during
the last week of April to the first week of May, and nesting is nearly synchronous among
females in a population. The eggs most frequently are found attached to the
undersides of rocks and logs in flowing water. In Lake Minnewaska, however, Bahret
(1996) found clutches on the topmost leaves of water moss and not deposited cryptically.

ii. Clutch sizes. In Massachusetts, I.W. Wilder (1924b) found that the usual
complement was 12–36 with an average of 18. In New York, Noble and Richards
(1932) reported a maximum of 41 eggs, and Bishop (1941b) found a maximum of 43 eggs with
a mean of about 30. Stewart (1968) examined the number of enlarged ovarian
follicles in New York specimens and found 19–86, with a mean of 46 follicles.
However, some ovarian follicles may not mature, so follicle counts probably overestimate
the number of eggs ovulated and fertilized. Often times, > 1 nest can be found
under a single large rock. One should consider strongly the possibility that any
nest that contains > 50 eggs likely represents the complements of > 1 female.
The female stays with the eggs; I have found females guarding eggs that were nearly
ready to hatch. Incubation period is 4–10 wk (Petranka, 1998).

C.
Larvae/Metamorphosis. Larvae are aquatic; excellent descriptions and illustrations
are provided by Trapido and Clausen (1940) for specimens from Québec and by Bishop
(1941b) for specimens from New York.

i. Length of larval stage. For New York stream populations, the larval period is
generally 2 yr with a mean size of 30 mm SVL (45.7–80.0 mm TL) at metamorphosis
(Stewart, 1968). In Pennsylvania, some individuals take 3 yr to metamorphose, but
despite whether 2 or 3 yr are necessary, metamorphosis occurs at 27.1–34.1 mm SVL
and 54.6–60.9 TL (Hudson, 1955). Trapido and Clausen (1940) reported that in
Québec the larval period in streams may be 3 yr and the smallest metamorphosed
individual was 77 mm TL. Larvae from still waters seem to attain a larger size than
those from streams. For example, the largest larvae Bahret (1996) collected from
Lake Minnewaska were 43–46 mm SVL and 84–92 mm TL. Whether the larger
size of these larvae is due to a longer larval period is unknown.

ii. Larval requirements.

a. Food. Smallwood (1928) stated that the larvae of northern two-lined salamanders
from the Onondaga Mountains of New York eat caddisfly larvae and beetle larvae.
Burton (1976) reported the most important food items found in larvae from a New Hampshire
stream are midges, stoneflies, cladocerans, and copepods.

b. Cover. At night I often have observed northern two-lined salamanders larvae at
the bottoms of shallow, quiet pools that form below riffle areas in rocky streams.
At these times, the larvae are either stationary on the substrate or slowly crawling
along the bottom. Larvae can be found in such pools in the daytime as well, but
usually then they are found under sticks, leaves, and other debris that accumulate in
areas of such pools. Larvae also are collected frequently after scrapping through
rocks and logs in riffles and holding a dip-net downstream from the disturbance.
Hudson (1955) in southeastern Pennsylvania noted that larger larvae are less secretive
than smaller larvae. Larvae are prone to drift downstream (Johnson and Goldberg,
1975), which might be an important factor in the extraordinary dispersal ability of this
species.

iii. Larval polymorphisms. Unknown.

iv. Features of metamorphosis. Some observations suggest that a great deal of
variation occurs in the time to metamorphosis within a given cohort, independent of
environmental factors. In Massachusetts, I.W. Wilder (1924a) noted that the
majority of larvae pass through their second winter in a pre-metamorphic state, whereas
others lag behind a year. Transformation occurs as early as May in the 2-yr-old
pre-metamorphic group, reaches its height in July, and continues into early fall.
Laggards from this group may pass through a third winter. Elsewhere, I.W. Wilder
(1924b) reported that two individuals, hatching at the same time in the laboratory and
kept under the same conditions, metamorphosed at dates approximately 1 yr apart. My
own observations lead me to believe that metamorphosis may occur more synchronously in
some populations. In late summer and early fall, I often find a marked increase in
the number of recently transformed juveniles under rocks along woodland streams.

v. Post-metamorphic migrations. Juveniles apparently stay close to streams through
their first breeding season, which may occur in the spring following metamorphosis in the
previous autumn (Bishop, 1941b). MacCulloch and Bider (1975) in Québec found
that metamorphosing individuals in August remained closer to their natal streams than
post-breeding adults.

vi. Neoteny. Neoteny is not known to occur. Cope (1889) noted, “It is
one of those species whose metamorphoses are prolonged and which remains in the larval
state until nearly fully grown.” Thus, large larvae often possess
well-developed gonads, and, as proposed by Bishop (1941b), maturity may be attained
within a comparatively short time after transformation.

D. Juvenile
Habitat. As indicated above, juveniles rapidly mature into adults, and if
metamorphosis occurred in a given stretch of a stream, juveniles occupy that area through
their first breeding season. A brief post-larval migration into terrestrial
habitats < 100 m from the stream may occur (MacCulloch and Bider, 1975). Thus,
the requirements during this short juvenile stage are not different from adults.

E. Adult
Habitat. Adults from various populations of northern two-lined salamanders are
28.9–40.9 mm mean SVL; the record individual is a female 53 mm SVL and 123 mm TL
from Ohio (Sever, 1999a). Stewart (1968) reported that females from New York are
significantly longer than males. Two-lined salamanders usually are the smallest
species when they occur in communities containing other salamanders in the northeastern
United States. The primary habitats are unpolluted bogs, springs, streams, or
lakes in wooded areas. Most small streams in the wooded, mountainous areas of the
range are rocky, which provides a good substrate for nesting, and lack large predatory
fish. Occasionally, specimens are found along larger streams and rivers, but
nesting has not been reported in such habitats. Although members of the northern
two-lined salamander complex can co-exist in streams with predatory fishes (Petranka et
al., 1987), predation by fish still is a factor that likely limits extensive exploitation
of rocky areas along large streams. Lake Minnewaska, where Bahret (1996) found
nesting at depths of 9–13.5 m and adults living year-round at 18 m, lacks
fish. The disappearance of fish is attributed to atmospheric acid deposition in the
lake during the early 1900s, resulting in a pH of 4.5 (Bahret, 1996). This high
acidity, however, seemingly does not affect success of northern two-lined
salamanders.

F. Home Range
Size. Stewart (1968) found as many as 11 adults/m2 in New York populations,
whereas Burton and Likens (1975b) reported only 0.02–0.04 individuals/m2 in
the Hubbard Brook Experimental Forest of New Hampshire. These densities seem quite
disparate in populations that presumably occupy favorable habitats. Density studies
on terrestrial northern two-lined salamanders, however, can be confounded by influx of
numerous newly metamorphosed juveniles in late summer and fall, aggregations in spring of
adults at favorable mating/nesting sites, interspecific interactions, and/or other
factors.

K. Interspecific
Associations/Exclusions. As noted previously, in much of the Canadian range,
especially north of the St. Lawrence Seaway and the Great Lakes, northern two-lined
salamanders are the only stream-side salamanders. In more southern portions of its
range, northern two-lined salamanders share stream habitats with one or more of the
following species: long-tailed salamanders (Eurycealongicauda),
northern dusky salamanders (Desmognathusfuscus), Allegheny Mountain
dusky salamanders (Desmognathusochrophaeus), red salamanders
(Pseudotritonruber), and/or spring salamanders (Gyrinophilusporphyriticus). The latter species is a known predator of northern
two-lined salamanders (Wright and Haber, 1922; Bishop, 1941b). No detailed studies,
however, have been done on ecological interactions between northern two-lined salamanders
and these species. Studies are also necessary on the ecological and genetic
relationships of northern two-lined salamanders and southern two-lined salamanders in
areas of sympatry in Ohio, West Virginia, Virginia, and Maryland.

L. Age/Size at
Reproductive Maturity. As mentioned earlier, metamorphosis generally occurs in the
summer or fall of the second or third year, and these individuals may reach sexual
maturity in time to participate in breeding activities the following spring. As a
result, individuals are breeding at the beginning of their third or fourth year,
depending upon length of the larval period. The smallest mature specimens I have
examined were 30 mm SVL; however, I examined two males 25 mm SVL from Chittenden County,
Vermont, that had evenly pigmented testes and may have been mature. Bishop (1941b)
reported that sexual maturity is reached in males at 67 mm TL and some females when only
61 mm TL.

M. Longevity.
In Québec, MacCulloch and Bider (1975) reported that only 25% of post-breeding
adults who migrated > 100 m from the mating/nesting area returned for the subsequent
breeding season. They attributed this loss of 75% of these migrants to mortality,
which indicates a rather high turnover in the adult population each year. I am
unaware of any literature on maximum life span either in nature or in captivity.

N. Feeding
Behavior. Feeding habits of metamorphosed northern two-lined salamanders have been
studied by Surface (1913) in Pennsylvania, Smallwood (1928) and Hamilton (1932) in New
York, and Burton (1976) in New Hampshire. As expected, a wide range of invertebrates
are eaten, although Burton (1976) noted that prey items are primarily terrestrial.
Terrestrial items include various insects (beetles, roaches, springtails, dipterans, and
hymenopterans), earthworms, snails, spiders, and isopods, whereas aquatic prey includes
stonefly nymphs, caddisfly larvae, midges, and mayflies. Thus, northern two-lined
salamanders are generalist feeders that are likely to eat any small invertebrate within
the appropriate size range.

O. Predators.
Wright and Haber (1922) included northern two-lined salamanders among other salamander
species that are preyed upon by spring salamanders. Bishop (1941b) noted that a
number of recently captured spring salamanders from New York disgorged partly digested
specimens of northern two-lined salamanders. Other known predators include shrews,
owls, blue jays, garter snakes, and trout (Brodie, 1977; Petranka, 1998). I have
observed screech owls (Otusasio) capturing northern two-lined
salamanders on blacktop roads on rainy nights.

P. Anti-Predator
Mechanisms. Brodie (1977) reported that northern two-lined salamanders assume a
defensive posture when attacked by shrews (Blarinabrevicauda) and blue
jays. The body is coiled with the head near the vent, and the tail is elevated and
undulated. In a test chamber, 10 of 11 northern two-lined salamanders attacked by
shrews were first bitten on the tail. The shrew backed away, wiping its mouth,
which in nature could give the salamander time to escape (Brodie, 1977). In a later
study in which northern two-lined salamanders from New York were exposed to shrews, only
26% of the salamanders survived attacks (Brodie et al., 1979). In some cases, the
tail was contacted by the shrew and avoidance followed, but in other cases, the head was
bitten before the tail was contacted. The shrews, however, did not eat 47.8% of
the northern two-lined salamanders killed, indicating that shrews find the salamander
relatively unpalatable (Brodie et al., 1979). Dowdey and Brodie (1989) studied
anti-predator response of northern two-lined salamanders from New York to garter snakes
(Thamnophis sp.). Garter snakes are predators that are not repulsed by
skin secretions, and salamanders do not assume the defensive postures used against blue
jays and shrews. Instead, northern two-lined salamanders run or remain immobile
during encounters with garter snakes. In a testing chamber, most salamanders ran
when flicked by a snake's tongue, and 90% of these with tails survived (tailed
individuals ran faster than tailless ones). All salamanders that remained immobile
after tongue flicks were eaten. The response to running was well developed only in
a population subjected to heavy snake predation. However, when a salamander was
merely contacted by the head or body of a garter snake, most remained immobile and 100%
of these survived. Only 34% survived of those who ran. In an experiment using
Pennsylvania specimens, Whiteman and Wissinger (1991) found that northern two-lined
salamanders (59%) were almost twice as likely to autotomize their tails when attacked by
garter snakes than northern dusky salamanders (24%) or Allegheny Mountain dusky
salamanders (28%). Tail autotomy can increase the chance of the salamander
escaping, although it makes the animal more susceptible to future predator attack (Dowdey
and Brodie, 1989). Two-lined salamanders, therefore, have alternative
anti-predator strategies, and the type and efficacy of each strategy varies with the type
of predator and, in the case of garter snakes, the nature of contact.

Q. Diseases. I
am not aware of any reports on diseases of northern two-lined salamanders.

R. Parasites.
I am not aware of any reports on parasites of northern two-lined salamanders. Some
literature on this subject (Burchett and Shoemaker, 1990) does exist for the sister
taxon, southern two-lined salamanders.

S. Comments. A
considerable literature exists on northern two-lined salamanders, and Sever (1999a)
should be consulted for additional references, especially on topics not covered here such
as morphology, physiology, and diagnostic characters. Note especially that several
recent accounts (e.g., Petranka, 1998, Powell et al., 1998) continue to use characters
like tail stripe length and number of costal grooves between toes of the adpressed limbs
to separate species in the complex, even though such characters have long been
discredited (Sever, 1972, 1989, 1999a,b,c). Because Petranka (1998) did not
recognize southern two-lined salamanders and Blue Ridge two-lined salamanders as separate
species, he combined data on these species with those on northern two-lined salamanders
into one account; a careful reading, however, will reveal much material relevant to each
taxon.

4. Conservation. Northern two-lined salamanders are listed as Protected by the
State of New Jersey (Levell, 1997). This categorization applies to all indigenous
non-game species in this state and does not necessarily indicate a conservation
concern. In general, northern two-lined salamanders are widespread and suitable
habitat is available across their range. Indeed, northern two-lined salamanders
may be spreading their range north.